Most helicopters have a small rotor placed vertically at the tail of the aircraft, which rotates continuously.
This has two main purposes: it prevents the helicopter fuselage from turning in circles continuously, and it is also used to control the helicopter’s direction when it is being flown.
Without a Tail Rotor, a Helicopter Would Turn in Circles!
To make a helicopter fly, the pilot raises the collective and increases the lift on the rotor blades in order to lift the helicopter into the hover. However, this causes a definite problem.
If the blades are whirling anti-clockwise, as most helicopter blades do, the fuselage will start to rotate clockwise, due to torque reaction. This is due to Newton’s Third Law, which states that every action has an equal and opposite reaction. If you haven’t heard of this, one of the easiest ways of explaining it is to imagine a boat moored close to the shore. If you are in the boat and push on the land, the land doesn’t move, but the boat does!
This is an example of Newton’s Third Law.
In the case of the helicopter, what can we do about this? Actually there are several ways of solving the dilemma. You can have two rotors that spin in opposite directions, as in the Chinook, and more recently, designers have experimented with blowing air out of ducts onto the tail boom to push it back, as it were.
But the most common method of preventing the fuselage spinning uncontrollably is to have a tail rotor. A small version of the main rotor, this is mounted vertically at the end of the tail cone, and it effectively works by pushing the tail back as the fuselage tries to rotate. It is like a sideways rotor system, and the air being forced down between the blades is used to push the fuselage straight.
Using the Tail Rotor to Turn the Helicopter
We now also have a useful way of controlling the helicopter in yaw, that is movement around a vertical axis. This is done by altering the pitch angle of the tail rotor blades, ie changing by a small amount the degree of force or turning motion which they produce. This is done by means of the pedals, which are certainly not rudder pedals, as some fixed-wing pilots mistakenly believe. The pedals are designed so that applying the left pedal turns the helicopter left, and applying right pedal turns it right.